Electron type fluorescent display device with planar adjacent control electrode

ABSTRACT

An electron tube having at least two electrodes and a cathode disposed within an evacuated envelope. One of the electrodes is spaced generally transversely with respect to the electro beam path from the cathode to the other electrode. The electrode which is spaced from the electron beam path is used to control the cathode current. Means are provided to couple various voltages to the respective electrodes to accomplish the desired control. The anode electrode may have a phosphor coating thereon so as to glow when bombarded by an electron beam from the cathode. Accordingly, an electron tube of this type is adaptable to display units for the display of letters, symbols, numerals and the like. In one form of the invention, the anode electrode and the control electrodes are arranged in a predetermined pattern to cause elemental areas of the anode electrode to glow and produce a display.

United States Patent Shimada June 6,1972

[54] ELECTRON TYPE FLUORESCENT DISPLAY DEVICE WITH PLANAR ADJACENT CONTROL ELECTRODE [72] Inventor:

[73] Assignee: Sony Corporation, Tokyo, Japan [22] Filed: Apr. 13, 1970 [21] Appl.No.: 27,713

Satoshi Shimada, Tokyo, Japan Archer et a1.. ...3 1 5/1 69 TV Weidel et a1 ..313/109.5

4/1970 'lanji ..3l3/l09.5 10/1970 Akabaneetal ..3l3/l09.5

[5 7] ABSTRACT An electron tube having at least two electrodes and a cathode disposed within an evacuated envelope. One of the electrodes is spaced generally transversely with respect to the electro beam path from the cathode to the other electrode, The electrode which is spaced from the electron beam path is used to control the cathode current. Means are provided to couple various voltages to the respective electrodes to accomplish the desired control. The anode electrode may have a phosphor coating thereon so as to glow when bombarded by an electron beam from the cathode. Accordingly, an electron tube of this type is adaptable to display units for the display of letters, symbols, numerals and the like. in one form of the invention, the anode electrode and the control electrodes are arranged in a predetermined pattern to cause elemental areas of the anode electrode to glow and produce a display.

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ATTORNEYS m BACKGROUND OF THE INVENTION Field of the Invention The field art to which this invention pertains is electron tubes and in particular to electron tubes which are useful for the purpose of presenting a display of a letter, numeral, or other symbol.

I I SUMMARY OF THE INVENTION It is an important feature of the present invention to provide an improved electron tube.

It is another feature of the present invention to provide an electron tube having at least two electrodes and a cathode sealed in an evacuated envelope.

It is a principal object of the present invention to provide an electron tube having a control electrode which is spaced generally transversely of the electron beam path between the cathode and another electrode.

It is also an object of the present invention-to provide an electron tube having at least two electrodes disposed generally in a plane wherein one of the electrodes is used to control the current received by the other electrode.

It is the further object of the present invention to provide an electron tube as described above wherein the anode electrode is coated with a luminescent material and is caused to glow when bombarded with an electron beam from the cathode.

It is an additional object of the present invention to provide an electron tube which is capable of being used as a display unit to produce a display of letters, numerals, symbols or the like.

It is another object of the present invention to provide an electron display tube as described above wherein the control electrodes are spaced transversely relative to the electron beam and are used to control the electron beam delivered to elemental portions of the phosphor coated electrodes.

It is also an object of the present invention to provide an electron display tube as described generally above wherein the phosphor coated electrodes thereof are arranged generally in a figure 8" pattern.

These and other objects, features and advantages of the present invention will be understood in greater detail from the following description and the associated drawing wherein reference numerals are utilized to designate a preferred embodiment.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematicdiagram showing the principle of an electron tube of this invention;

FIGS. 2A and 3A are plan views respectively showing fundamental constructions of the electron tube of this invention;

FIGS. 28 and 3B are cross-sectional views respectively taken along the lines II--Il and Ill-III in FIGS. 2A and 3A;

FIG. 4 is a plan view schematically showing one example of this invention as being applied to an amplifier;

FIG. 5 is a circuit connection diagram of the amplifier depicted in FIG. 4;

FIG. 6 is a diagrammatic plan view illustrating another example of this invention as being applied to a flipflop circuit;

FIG. 7 is a circuit connection diagram of the flip-flop circuit shown in FIG. 6; 7

FIGS. 8 and 9 are respectively a top plan and a perspective view schematically illustrating other examples of this invention when employed as active elements;

FIGS. 10 and 11 are respectively a perspective and a crosssectional view schematically showing modified forms of this invention;

FIG. 12 is a plan view diagrammatically illustrating one ex- FIGS. 14 and 15 diagrammatically illustrate in cross section modified forms of the indicator tube produced according to this invention;

FIG. 16 is a plan view schematically showing the principal part of the indicator tube of FIG. 15;

FIG. 17 is a schematic diagram showing another modification of the indicator tube made up of the electron tube of this invention;

FIG. 18 is a plan view for explaining one example of a method for the manufacture of the indicator tube;

FIG. 19 is a cross-sectional view taken along the line XIX XIX in FIG. 18;

FIGS. 20 and 21 are respectively a plan and a side view illustrating the manner in which an indicator electrode unti assembly is sealed up in an envelope; and

FIGS. 22 to 32, inclusive, respectively illustrate in cross section other examples of the electron tube of this invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT This invention relates to an electron tube which has many applications as an active element such as in an amplifier, a switching circuit, a digital logic circuit or the like and also to an indicator tube for providing a display of numerals, letters, symbols or the like and, further, to a picture display device. The electron tube of this invention is simple in construction, small in size and easy to manufacture.

The electron tube of this invention comprises at least two electrodes arranged in substantially the same plane and a cathode. These electrodes and cathode are placed in a vacuum envelope and arranged so that current from the cathode is controlled by a voltage applied to at least one of the electrodes.

Referring to the drawings in further detail, a first electrode A (FIG. 1) is provided and elements G and G are insulated from the electrode A and arranged in substantially the same plane. The elements 6,, and G are interconnected by a lead to form a second electrode G. A cathode K is placed oppositely of the electrodes A and G.

The electrode A is used as an anode, which is supplied with a predetermined positive voltage, and the cathode K is grounded. The electrode G is used as a control electrode which is supplied with a predetermined voltage. With this voltage, a composite electric field established between the anode A and the cathode K is controlled, thereby to control the current emitted from the cathode.

When a small negative voltage is applied to the control grid and assuming that the composite electric field formed by the negative voltage and the voltage impressed on the anode A is positive, electrons generated by the cathode K are derived therefrom and directed to the anode A. The resulting current varies with the magnitude of the voltage applied to the control electrode G. Where the absolute value of the negative voltage impressed on the control electrode G is relatively great and the composite electric field established by the above voltage and the voltage fed to the anode A is negative, there is no anode current.

Consequently, a switching operation can be achieved by the voltage applied to the control electrode G and, in addition, an input signal voltage fed to the control electrode G can be amplified.

In the electron tube of this invention the cathode current is controlled by the composite electric field which is established by the voltages impressed on a plurality of electrodes. The

' functions of the electrodes A and G can be interchanged.

ample of an indicator tube made up of the electron tube of this invention;

FIGS. 13A, 13B, 13C are waveform diagrams showing signals to be applied to the indicator tube of FIG. 12;

Namely, it is possible to use the electrode G as the anode to be supplied with the positive voltage and cause the current between the anode G and the cathode K to vary with the voltage impressed on the electrode A which is then used as the control electrode.

Further, the cathode K may be pinhead shaped, strip-like or plate-like and any number of cathodes may be used.

If the surface of the anode A facing the cathode K is coated with a phosphor material such as ZnO, ZnS or the like, the phosphor material can be made luminescent by selecting the voltage applied to the control electrode G. According to my experiments, in a case where the anode A and the elements G and G were each 0.3 mm wide; the distances between the anode A and the elements G and G were 0.4 mm; the distance between the anode A and the cathode K was mm; and a voltage of +70 to 80 volts was impressed on the anode A with a positive voltage applied to the electrodes G and G the phosphor material glowed completely. When a voltage of 50'or less was impressed on the elements G and G the phosphor material did not glow.

Accordingly, an indicator tube for providing a display of a number, character, symbol or the like and a picture display device can be produced by the use of the electron tube of this invention. By supplying the anode A with a high positive voltage and the control electrode G with a lower voltage, only the anode A is lighted even if the control electrode G has been coated with the phosphor material.

In the making of such an electron tube the anode A and the control electrode G are deposited on an insulating base plate S (FIG.'2A) such as alumina, forsterite, ceramic, glass or the like, and the resulting assembly is placed in a vacuum envelope.

In FIG. 2A rectangular electrodes G and G are shown to be interconnected by a lead L A rod-like cathode K is disposed above the anode A in parallel relation thereto.

In FIGS. 3A and 3B an annular control electrode G is disposed on the outside of a circular anode A, and a cathode K is disposed above the center of the anode A. In this case the cathode K is secured to the base plate S by suitable means.

FIG. 4 schematically shows a multistage amplifier employing the electron tube of this invention as an amplifier element in each stage, and FIG. 5 is a circuit connection diagram of the amplifier. In this case the amplifier elements of the respective stages are formed on a common insulating base.

An amplifier element X, of a first stage comprises an anode A, and a control electrode G, formed by interconnected elements G, A and G, B disposed on both sides of the anode A,. An amplifier element of the next stage is similarly comprised of an anode A and a control electrode G, consisting of interconnected elements G and G arranged on both sides of the anode A An amplifier element of the output stage comprises an anode A consisting of three interconnected electrodes A to A and a control electrode G consisting of four interconnected elements G to G disposed on both sides of each of the electrodes A to A Further, resistors R R R R and R are used on the same base and an electrode T, is formed on the underside of the element G through a suitable dielectric to provide a coupling capacitor C,. An electrode T is similarly formed on the underside of the element G to provide another coupling capacitor C and electrodes T to T are respectively formed on the undersides of the elements G to G and are interconnected to provide a coupling capacitor C,,. An input terminal I, an output terminal 0 and terminals B, K and C are to be connected to the plus and minus sides of a power source. A strip-like cathode K is disposed above the electrodes and extends as shown. The resulting assembly is sealed in a vacuum envelope.

With an input signal being applied to the input terminal I and a load connected between the terminals B and O, the amplifier of the above arrangement can be caused to perform exactly the same amplifying operation as a usual amplifier using vacuum tubes or transistors. The functions of the electrodes A, to A and those of the electrodes G, to G in the amplifier elements X, to X, can be interchanged as indicated above.

FIG. 6 illustrates a flip-flop circuit employing the electron tube of this invention as an active element and FIG. 7 is its circuit connection diagram. Active elements, of the sameconstruction as those X, and X in FIG. 4 are formed on a common base, and electrodes T,, T and T are respectively deposited on the undersides of elements G G and G through dielectric members to form capacitors C,, C, and C,. Resistors R R R and R a trigger input terminal T, a terminal B connected to the plus side of a power source, a ground terminal E and an output terminal P are provided as shown. A strip-like cathode is disposed opposite the electrodes, and the resulting assembly is sealed in a vacuum envelope. In this case, if a luminescent material is coated on anodes A, and A, of both active elements X, and X,, the anodes of the elements glow when switched on," so that it can be detected visually which element is in the on state.

When the electron tube of this invention is used as an active element, especially in cases where many circuits are required, such constructions as shown in FIGS. 8 and 9 can be employed. In FIG. 8 elements and circuits are formed on both sides of a base plate S shaped in the manner of a folding screen and cathodes K are each provided in common to the elements formed on opposing surfaces of adjacent plate portions. In FIG. 9 a plurality of base plates, each having elements and circuits formed on both sides thereof, are disposed side by side in parallel relation to one another, and common rod-like cathodes K are each disposed between adjacent bases.

The so-called hybrid integrated circuit device can also be produced by mounting a semi-conductor device on the base.

The electron tube of this invention may be of a construction shown in FIG. 10 in which an anode A and electrodes G and G of an annular configuration are formed on the inner wall of a cylindrical base S, and a rod-like cathode K is disposed atthe axis of the cylinder. It is also possible to adopt a construction depicted in FIG. 11 in which the anode A and electrodes G A and G are formed on the inner wall of a ring'shaped base plate S, and a pinhead-like or strip-like cathode K is placed at the axis thereof.

In short, the electrodes need not always be placed in exactly the same plane, but may lie in slightly offset planes.

In FIG. 12 there is illustrated an example of the electron tube of this invention as applied to an indicatortube of a matrix-like construction. Namely, one indicator electrode unit or a display unit 1 is made up of a first electrode group consist ing of a plurality of first electrodes A, to A, which extend parallel to one another, and are arranged in substantially the same plane. A second electrode group consisting of a plurality of second electrodes G to G which extend, for example, vertically parallel to one another and which are arranged in substantially the same plane above the first electrode group while being insulated therefrom. A third electrode group consisting of a plurality of third electrodes G to G which extend vertically intermediate between adjacent second electrodes G to G and are insulated from the first and second electrode groups. In this indicator tube the first electrodes A, to A are sequentially arranged in common with the respective display units. The second electrodes G, to G,,,, of each unit are interconnected by a common lead I..,,-,, and the third electrodes G and G are respectively connected to selector leads L to L The first electrodes A, to A are coated with a phosphor material, and a common cathode K (not shown) is disposed above the respective display units.

In this case the minimum unit area caused to glow is a portion of each of the first electrodes defined by the space between adjacent electrodes of the second electrode group and respective electrodes of the third electrode group. Accordingly, each display unit has 35 luminescent units, and these luminescent units are selectively caused to glow to provide a display of a predetermined numeral, letter or the like.

The luminescent units are lighted by impressing a positive predetermined voltage to the second electrodes and applying a positive predetermined voltage to those electrodes of the first and third electrode groups which correspond to one another.

The second electrodes G, to G are supplied with a voltage E through the lead 1. for a time T as shown in FIG. 13A. In a first period T, (FIG. 13C), which is one-fifth of the time T, the electrode G is supplied with a voltage E and the electrodes A and A, are respectively supplied with a voltage E, as depicted in FIGS. 13B and 13C. In a second onefifth period T (FIG. 13C), the electrode G is supplied with the voltage E and the electrodes A,, A and A, are supplied with the voltage 15,. In a third one-fifth period T the electrode G is supplied with the voltage E and the electrodes A,, A and A, are supplied with the voltage E,,. In a fourth one-fifth period T,,, the electrode G is supplied with the voltage E and the electrodes A,, A and A, are supplied with the voltage E,,. In the last one-fifth period, T,,, the electrode 6 is supplied with the voltage E and the electrodes A A and A, are supplied with the voltage E,,. Thus causing predetermined luminescent units on the electrodes A, to A, to glow from left to right sequentially in a time divisional manner to provide a display of a numeral 2 in the entirety of the display unit. In this manner, desired numerals, letters, or symbols can be sequentially indicated by the respective display units. In this case, if the leads L L to L are provided on the back of the base, the indicator tube can be made correspondingly smaller in size.

In the illustrated example the second and third electrode groups are arranged perpendicular to the first electrode group but they need not always cross the latter at right angles thereto and may cross obliquely. Further, as will be apparent from the description in connection with FIGS. 1 to 3, the indicator tube need not always be comprised of three electrode groups but may be formed with two electrode groups.

The electrode A which is coated with a luminescent material may be in the form of a sheet metal as shown in FIG. 14. In this case parallel electrodes G,, 6,, G are formed substantially flush with one another on one surface of the sheet electrode A through insulating layers 1,, I 1 as of mica, glass or the like and a phosphor material is laid down on those areas of the electrode A which are defined between adjacent electrodes G,, G as indicated by 4,, 4 A cathode K is located opposite the electrodes, and the resulting assembly is sealed in a vacuum glass envelope 3.

A phosphor area may be formed separately as exemplified in FIGS. 15 and 16. The figures illustrate an indicator device of the same construction as that of a shadow mask color picture tube. Reference character A indicates a sheet metal having bored therein apertures H,,, H H H H H H H H sequentially arranged in a lateral and a vertical direction. On one surface of the apertured sheet metal A a plurality of parallel electrodes G,,,, G G are provided adjacent to insulating layers 1, 1, thus constituting a first electrode group. On the other surface of the sheet metal a plurality of parallel electrodes G G G are provided adjacent to insulating layers 1 I I thus constituting a second electrode group. The resulting assembly is sealed in a vacuum glass envelope 3, and a suitable number of cathodes K,, K K are disposed in the envelope 3 at suitable locations.

A phosphor material is coated on the inner wall of the envelope 3 on the opposite side from the cathodes, providing a phosphor area 4. The phosphor area 4 is caused to glow at desired locations by selectively applying a positive voltage to the electrodes 6, G G G under such conditions that the sheet metal A is supplied with zero or positive voltage, and the phosphor area 4 is supplied with a high voltage. When a predetermined positive voltage is applied to the electrodes, for example, G, and G G,,, and G the cathode current passes through the aperture H,, surrounded by these electrodes and impinges upon the phosphor area 4 to cause it to glow at a location under the aperture 11. Applying a predetermined positive voltage to the electrodes, for example, 0, and G the currents from the cathodes K, and K pass through the four apertures H,,, H,,, B and H near the electrodes and strike the phosphor area 4 to light it at positions just under the apertures. Consequently, not only numerals, letters, symbols or the like but also pictures can be displayed by sequential radiation of the phosphor area at predetermined positions and, further, the display can be provided in color.

In the above example the apertures are aligned in rows and in columns and the electrodes G G and G G are arranged to extend perpendicular to each other, but these electrodes may be oblique to each other as well.

In FIG. 17 the indicator electrode unit is made up of a plurality of indicator electrodes arranged in the form of a number 8" and is designed to indicate any number 0" to 9" by selective radiation of the indicator electrodes. Seven strip-like indicator electrodes A, to A, are arranged on an insulating base in the form of the number 8, and a dot-like electrode A for decimal indication is located in the vicinity of the foot of the assembly. Another electrode G (FIG. 18) surrounds the electrodes A, to A,. Such display units are sequentially aligned along the length of the base. The electrodes A, to A, may be formed by means of printing and baking of a conductive paint containing silver powder or the like, and by etching or punching of sheet metal or the like. The electrodes A, to A are respectively connected through leads 6, to 6 to selector leads 10, to 10,, extending in the direction of array of the display units, and the electrode G is connected to a lead 6 Then, a phosphor material is coated on the surfaces of the electrodes A, to A and a common cathode K is disposed opposite the indicator electrode units.

By applying a positive voltage of, for example, 20 volts to predetermined ones of the electrodes A, to A under such conditions that the electrode G is supplied with a voltage of -20 to l00 volts, composite electric fields established near the electrodes supplied with the positive voltage are made positive. Therefore, these electrodes glow to display a desired number. Application of a positive voltage to the electrodes, for example, A,, A A A, and A, leads to a display of a number 3 and application of a positive voltage to the electrodes A,, A A, and A results in the display of a number 7.

In this case it is also possible to coat the phosphor material on the electrode G for lighting the surrounding area of a number being displayed in such a manner that a number, for example, 8 is displayed by lighting only the electrode G and O is indicated by lighting the electrodes G and A.,.

By providing the selector leads 10, to 10,, on the opposite surface of the base plate on which are formed the electrodes A, to A and G, the base plate can be narrowed correspondingly.

In the construction of such an indicator device it is preferred that a driving device for actuating the indicator device be also enclosed in the glass envelope together with the indicator assembly.

Referring now to FIGS. 18 and 19, a description will be made of one example of the way of making such indicator tubes. The manufacture begins with the preparation of an insulating base 5 formed of, for example, alumina, ceramic, forsterite, glass or the like. On one surface of the insulating base 5 seven strip-like electrodes A, to A, are arranged in the form of a number 8," and a dot-like electrode for decimal indication is disposed in close proximity to the foot of the assembly. Further, leads 6, to 6,, for connecting the electrodes A, to A to selector leads are extended to the marginal portions of the base plate 5, and a lead 6 is formed for leading out another electrode which surrounds the electrodes A, to A Display units, each having the electrodes A, to A and the leads 6, to 6 are sequentially located along the length of the base plate 5. In addition, terminals 7, to 7,, are provided for external connection of the selector leads. Electrodes A, to A and the leads 6, to 6 and terminal 7, to 7,, may be formed by means of printing and baking or, for example, silver paint, a molybdenum-manganese alloy or the like. The molybdenummanganese alloy is readily oxidized, so that when the electrodes and the leads are formed of this alloy, they are plated with nickel so as to prevent oxidation. Then, the surfaces of the electrodes A to A are coated with the phosphor material. Next, glass frit, for example, is coated by printing on the base plate 5 except on those areas where the electrodes A, to A have been formed and except on the end portion of the respectively connected at one end to the terminals 7,

base where the terminals 7, to 7 have been formed. Then the insulating base 5 is baked to form thereon an insulating layer 8. The insulating layer 8 is not formed on the electrodes A, to A,, but, in practice, the insulating layer 8 is formed across the electrodes A, to A, so as to join electrodes G which will be subsequently deposited on the insulating layer 8 inside and outside of the electrodes A, to A,.

In the insulating layer 8 small windows 9, to 9 are bored each just on one end of each of the aforementioned leads 6, to 6,, in such a manner that the ends of the leads are exposed through the windows9, to 9,. Then, the electrode G is formed on the insulating layer 8 surrounding the electrodes A, to A and selector leads 10, to 10,, are formed on the marginal portions of the base plate 5 which extend in the direction of array of the display units. In this case these-leads 10, to 10,, are to 7 Thus, the electrodes A, to A, are respectively connected to the terminals 7, to 7,, through the leads 6, to 6,, and selector leads 10, to 10,. Further, the electrode G is formed over the window 9,, too, and hence is connected to the lead 6 On the back of the base 5 a lead and its terminal are previously formed, so that the lead 6,, of the electrode G in each display unit is connected to the lead and terminal on the back of the base 5.

Thereafter, the electrodes G, the leads 10, to 10 and the terminals 7, to 7,, are coated with an opaque material to prevent their radiation. A common strip-like cathode is mounted by suitable means on the base 5 in opposing relation to the display units, though not shown, thus providing the plurality of display units, and the base 5 is sealed in a glass envelope.

It is preferred to seal the base 5 in a glass envelope 3 in a manner to project out therefrom the end portion of the base 5 on which are formed the terminals 7, to 7 for leading out the electrodes A, to A,,, and the lead on the back of the base plate 5 for leading out the electrode G, though not shown, as illustrated in FIGS. 20 and 21. In the event that the base 5 is formed of ceramic, glass or the like, the open end portion of the envelope 3 can be readily closed by applying to the open end Pyroceram cement (Trademark) made by Corning Glass Works, as indicated by 17' in FIG. 21. When the base plate 5 is thus sealed up in the glass plate 3 with the end portion 5a of the base plate 5 projecting out therefrom, the terminals 7, to 7 formed on the end portion 5a can be used as external leads. This eliminates a process for attaching external leads to the base and simplifies the placement of the base in the glass'envelope, which allows ease in the manufacture of the indicator tube, reduces the manufacturing cost and provides for enhanced mechanical strength, as compared with a method wherein external leads are connected to the terminals 7, to 7,, on the base 5 and the base 5 is entirely sealed in the glass envelope with the external leads partially projecting out therefrom.

A description will be given of examples of the method by which the electron tube of this invention used as an active element or indicator tube as above described is sealed in and attached to a vacuum container such as a glass envelope. In the drawings the active element or indicator tube is symbolically indicated by a base S and electrodes A and G formed thereon.

' The base having formed thereon the device may be entirely sealed in the vacuum envelope, but it is also possible that the base plate itself forms one portion of the envelope as shown in FIG. 22, in which a dish-like glass vessel 12 is mounted on the base plate S in a manner to cover the electrodes A and G. In this case the vessel 12 is secured at marginal portion to the base S by the use of, for example, fused glass frit, cement or the like.

In FIG. 23 one end portion of the base S projects out from an envelope l3, namely, the envelope 13 is scaled up at the projecting end portion of the base S, and a multi-connector socket I4 is engaged with the projecting end portion. Reference numeral 22 designates a support for mounting a cathode K on the base S. This method is possible in the case where the base is not an insulating plate but a metal plate as in FIGS. 14 to 16.

Where the base plate projects out from the glass envelope, the base plate and the glass envelope equally receive external heat, so that they are equally expanded and electrode leads L formed on the base plate can be used as external leads. Accordingly, this method lessons the number of steps in the manufacturing process, as compared with the case where external leads are connected to the terminals formed on the base and the external leads partially project out from the glass envelope.

The cathode need not always be located opposite the electrodes A and G but may be disposed, for example, substantially flush with the electrodes A and G as depicted in FIG. 24. In this case, although a dish-like glass vessel 12 is mounted on the base plate S by glass frit as in the case of FIG. 22, annular electrodes A and G are concentrically formed, with the electrode G being inside of A and a cathode K being disposed substantially flush with the electrodes A and G at their center.

In the case where the device is sealed in the vacuum envelope, the operation of the device is sometimes affected by a change in the internal electric field due to charge produced on the envelope wall, for example, by touching on the envelope by hand or due to an external electrostatic field. To avoid this, a transparent conductive coating, a mesh, netting or wire-like conductor as of graphite, aluminum or the like is deposited on the inner wall of an envelope l4 and is connected, for example, through a contact piece 16 to a lead formed on the base S and led out from the envelope, through which lead the conductor 15 is always held at a suitable potential.

FIG. 26 illustrates another modification in which a grid electrode is provided as indicated at 17 or 18 between the electrodes A and B in the vicinity of the cathode K, and the grid electrode is supplied with a predetermined voltage so as to promote emission of thermoelectrons. The grid electrode may be in a spiral form.

It is also possible to provide a plurality of cathodes and maintain them at difierent DC potentials, as depicted in FIG. 27 in which two cathodes K, and K are provided opposite the electrodes A and G. In this case, the cathode, for example K,, is held at ground potential; the cathode K is supplied with a voltage of 20 volts; the electrode, for example, G is held at ground potential; and the electrode A is supplied with a voltage of 50 to volts. With such potential distribution, electron currents from the cathodes K, and K are controlled by the composite potential on the electrodes A and G in such a manner that electrons are derived from the cathode K, at all times and that electrons are derived from the cathode K when the voltage applied to the electrode A exceeds a certain value. In this case it is also possible to vary the voltage fed to the electrode G or to vary the potential applied to the cathode, for example, K while holding constant the voltages applied to the electrodes A and G. FIG. 28 shows the case in which electrodes A,, A, and G,, G,, are provided on both sides of the base S while being respectively interconnected through apertures bored in the base S, and cathodes K, and K are located on both sides of the base plate S. The operation of this device may be achieved in the same manner as in the case of FIG. 27.

The constructions such as exemplified in FIGS. 27 and 28 are of particular utility when employed in amplifiers or the like.

The cathode may be a source of free electrons which are secondarily generated by heat, irradiation by light rays, electron rays, radioactive rays, X-rays, cesium or the like or highfrequency heating from the inside or outside of the envelope. In FIG. 29, a heater 19 is disposed near the cathode K and in FIG. 30 the cathode K is irradiated by the sun's rays through a lens 20. In short, the cathode may be of any type utilizing irradiation by light.

In the making of the indicator tube it is also possible to form the base S of semitransparent or transparent glass or like material and the electrodes A and G of a transparent conductive coating so that a number being displayed may be seen from the back of the base plate S, that is, from the opposite side from that where the electrodes A and G are formed, as indicated by the arrow. In such a case, the cathode K may be formed relatively large.

In FIG. 32 a conductor 21 for preventing the influence of charge on the envelope wall or external electrostatic field previously described with FIG. 25 is provided on the side of the base plate S where the electrodes A and G are formed so that the conductor 21 may not be noticeable when viewed from the back of the base plate S.

As will be understood from the foregoing, the electron tube of this invention has a wide range of applications as an active element in such circuits as amplifiers, switching circuits, digital logic circuits, and indicator tubes for displaying a number, letter, symbol or picture. Further, the electron tube of this invention is made up of at least two electrodes disposed in substantially the same plane and a cathode, and hence is very simple in construction, small and flat and easy to make.

I claim:

1. An electron tube comprising:

an evacuated envelope with at least one side transparent;

an insulating base mounted in said envelope such that at least part of a first side is visible through the transparent side of said envelope;

a first plurality of indicator electrodes mounted on the first side of the base and arranged in the form of a figure 8;

a second electrode of planar form mounted on said first side of said base and surrounding said first plurality of indicator electrodes and lying substantially in the same plane as said first plurality of indicator electrodes;

a cathode electrode mounted in said envelope adjacent said indicator electrodes and said second electrode;

a plurality of selector leads mounted on said base and respectively connected to said first plurality of indicator electrodes;

control means connected to said plurality of selector leads and adapted to selectively apply a voltage to said indicator electrodes which is positive relative to said cathode;

a second electrode lead mounted on said base and electrically connected to said second electrode, and said control means connected to said second electrode lead to selectively apply a voltage to said second electrode which can be switched between two values such that when at one value sufiicient current passes between said cathode and indicator electrodes to render said indicator electrodes visible and when at the other value insufficient current passes between said cathode and said indicator electrodes to render said indicator electrodes visible and wherein a layer of phosphor material covers said first plurality of indicator electrodes.

2. An electron tube according to claim 1 wherein opaque material covers said second electrode.

3. An electron tube according to claim 1 wherein a layer of phosphor material covers said second electrode in areas adjacent said first plurality of indicator electrodes.

4. An electron tube according to claim 1 comprising an auxiliary indicator electrode mounted on said base adjacent said first plurality of indicator electrodes, and an auxiliary indicator lead connected to said auxiliary indicator electrode and to said control means.

5. An electron tube according to claim 1 comprising a second plurality of indicator electrodes mounted on the first side of the base adjacent the first plurality of indicator electrodes and arranged in the form of a figure 8, a third electrode of planar form on said first side of said base adjacent said cathode electrode and surrounding said second plurality of indicator electrodes and lying substantially in the same plane as said second plurality of indicator electrodes, said first plurality of selector leads respectively connected to said second plurality of indicator electrodes, and a third electrode lead mounted on said base and electrically connecting said third electrode to said control means.

6. An electron tube according to claim 5 wherein a layer of phosphor material covers said second plurality of indicator electrodes. 

1. An electron tube comprising: an evacuated envelope with at least one side transparent; an insulating base mounted in said envelope such that at least part of a first side is visible through the transparent side of said envelope; a first plurality of indicator electrodes mounted on the first side of the base and arranged in the form of a figure 8; a second electrode of planar form mounted on said first side of said base and surrounding said first plurality of indicator electrodes and lying substantially in the same plane as said first plurality of indicator electrodes; a cathode electrode mounted in said envelope adjacent said indicator electrodes and said second electrode; a plurality of selector leads mounted on said base and respectively connected to said first plurality of indicator electrodes; control means connected to said plurality of selector leads and adapted to selectively apply a voltage to said indicator electrodes which is positive relative to said cathode; a second electrode lead mounted on said base and electrically connected to said second electrode, and said control means connected to said second electrode lead to selectively apply a voltage to said second electrode which can be switched bEtween two values such that when at one value sufficient current passes between said cathode and indicator electrodes to render said indicator electrodes visible and when at the other value insufficient current passes between said cathode and said indicator electrodes to render said indicator electrodes visible and wherein a layer of phosphor material covers said first plurality of indicator electrodes.
 2. An electron tube according to claim 1 wherein opaque material covers said second electrode.
 3. An electron tube according to claim 1 wherein a layer of phosphor material covers said second electrode in areas adjacent said first plurality of indicator electrodes.
 4. An electron tube according to claim 1 comprising an auxiliary indicator electrode mounted on said base adjacent said first plurality of indicator electrodes, and an auxiliary indicator lead connected to said auxiliary indicator electrode and to said control means.
 5. An electron tube according to claim 1 comprising a second plurality of indicator electrodes mounted on the first side of the base adjacent the first plurality of indicator electrodes and arranged in the form of a figure 8, a third electrode of planar form on said first side of said base adjacent said cathode electrode and surrounding said second plurality of indicator electrodes and lying substantially in the same plane as said second plurality of indicator electrodes, said first plurality of selector leads respectively connected to said second plurality of indicator electrodes, and a third electrode lead mounted on said base and electrically connecting said third electrode to said control means.
 6. An electron tube according to claim 5 wherein a layer of phosphor material covers said second plurality of indicator electrodes. 